The subject of the invention is a holding device for particulate material samples, especially a sample holder for particles with high fluid content like protein crystals.
Protein crystallography is a technique for analyzing the structure of proteins in which the latter are exposed to X-ray or synchrotron radiation in a crystallized state to enable conclusions about the molecular structure from diffraction patterns. The size and the irregular form of the protein molecules mean that protein crystals are characterized by very slight lattice forces and high solvent content in the region of 30 to 70% or even as much as 90%. Consequently protein crystals are unstable and restricted to characteristic crystal sizes between 0.003 mm and 1 mm. This instability is seen especially in the loss of crystal structure as soon as the crystal loses solvent through removal of water at room temperature.
It is generally known that protein crystals can be analyzed in a sealed capillary in the presence of free solvent to achieve adequate stability during structural analysis. A virtually saturated solvent atmosphere forms in the capillary, which prevents the crystallites from desiccating or drying. The disadvantage of this technique is that the crystallites in the capillaries are difficult to manipulate and that low-temperature treatment as protection against radiation damage in the protein crystal during structural analysis, as described for example in the publication by H. Hope in xe2x80x9cActa Cryst.xe2x80x9d (vol. 44, 1998, p 22 ff), is restricted in its application.
A holder for single protein crystals is described by R. Kiefersauer et al. in xe2x80x9cJ. Appl. Cryst.xe2x80x9d (vol. 29, 1996, p 311 ff). The conventional holder for the so-called free mounting system shown in FIG. 7 comprises in particular a holding capillary 41 arranged in a carrier block 42. One end of the holding capillary 41 is connected to a suction device (not shown) so that the inside of the holding capillary 41 can be subjected to a low pressure. The other end, projecting from the carrier block 42, forms a mount for the protein crystal. The advantage of this holder is that single protein crystals can be manipulated in the beam of the analyzer device. Nevertheless, special precautions are necessary to maintain crystal stability that restrict possibilities of manipulating the holder acting as a sample head. On the holder of the protein crystal at the end of the holding capillary 41, the crystal structure would change or dissolve rapidly at normal room conditions through the removal of solvent. For this reason a holder of this kind is operated in conjunction with a humidity feed (not shown in FIG. 7) where a humid stream of air is conducted to the held protein crystal through jets for example. The disadvantage of the humidity feed by separate jets is the more difficult manipulation of the holder, because the humidity jets have to be moved simultaneously without shadowing radiation of the crystal for instance.
A further disadvantage of the conventional humidity feed with jets is the more difficult control of the stream of gas actually exiting from the jets in relation to its humidity and flow conditions.
The indicated problems in holding protein crystals also occur in the manipulation of other particulate material samples with a high fluid content. These include biological objects like biological cells or cell constituents, and synthetic non-crystalline objects with a high solvent content. If objects of this kind are to be analyzed free of surrounding solvent, desiccation problems occur as described above in the case of protein crystals.
An object of the invention is to provide an improved holding device for particulate material samples with high fluid content that allows simplified manipulation of the samples, especially in analytical instruments and without restricting measurement functionality. Another object of the invention is also to propose novel and improved uses of such a holding device.
These objects are generally solved by a holding device for material sample particles with a carrier block for a holding element comprising e.g. a holding capillary or a loop holder, that has a free mounting end for a particulate sample, wherein the carrier block includes at least one integral gas channel with an outlet end that is directed at the mounting end of the holding element.
Accordingly, a holding device with a carrier block is created that includes not only a holding capillary, functioning in the way of vacuum pincers for example, or a loop holder but also at least one integrated gas channel that is directed at the mounting end of the holding capillary or the loop holder. The gas channel exits adjoining the holding element so that a local atmosphere is formed at the end thereof from gas or vapor flowing out of the gas duct. in a preferred implementation of the invention, the gas channel has an inner diameter that is greater than the outer diameter of the holding element, the latter being passed through the center of the gas channel so that the gas or vapor is fed through the gas channel in the remaining cylindrical space between the holding element and the edge of the gas duct. The holding capillary is surrounded by the gas duct.
In an especially advantageous or preferred form, the holding device according to the invention consists of a head part and an insert. The head part contains the gas channel, which a t the same time forms a lead-through for the holding capillary or the loop holder. The head part also forms a receptacle for the insert so that the latter can be shifted axially in the head part and fixed at a certain position. In this way the spacing of the end of the holding capillary or the loop holder, which forms a support for the particular material sample, from the exit of the gas channel or the surface of the carrier block can be altered in a predetermined way.
In the context of what is described here, a carrier block is any mechanical structure that allows the positioning and/or movement of a holding capillary or a loop holder. The holding capillary can be a hollow capillary operated with a vacuum (vacuum tweezer) or a compact, extended, pointed component with a support at its end for the particular material sample. Thus the invention is not restricted to implementation with the vacuum tweezer structure but can also be used with other holder devices in which the particulate material sample adheres to the tip of the holding capillary through the effect of adsorptive forces, electrical forces or an adhesive. An example for such an alternative holding device is the loop holder noted above which comprises a base part, a support part and the loop as such. Loop holders of this kind are known from protein crystallography or cryotransferring of samples. The term gas channel comprises every kind of gas feeder line. Several gas ducts may also be provided. The gas conducted in the gas channel will be, depending on application, a gas or a vapor with a certain content of vaporous substances that correspond to the fluid and/or added substances contained in the particular material sample. Thus it is possible for instance, to maintain certain surface properties on the material sample, to conduct a vaporous substance through the gas channel that differs from the fluid or solution in the sample.
The invention is associated with the following advantages. The carrier block of the invention with integrated gas channel allows improved and controlled manipulation of the sample. The disadvantage of shadowing in the measurement system through separate gas jets is avoided. The gas channel allows homogeneous and uniform feeding of the gas. Complete inclusion of the sample is guaranteed in all positions of the mounting device. Precise alterations of the sample are simplified. This affects both feeding added substances through the gas channel and the above mentioned low-temperature treatment, for example, as protection against radiation damage in protein crystals. The holding device according to the invention can be miniaturized. In an axial-symmetrical arrangement of the holding element, this will automatically be centered in the gas stream. The structure of the holding device according to the invention allows simplified adjustment in relation to a measurement setup. The number of interfering (e.g. scattering) components in the measurement range is reduced. The mounted sample is better accessible for additional measurement procedures (e.g. optical measurements).
For the first time the invention allows defined temperature setting in particulate material samples by setting the gas stream in the carrier block to a defined temperature. The sample immediately assumes the temperature of the gas because of its smallness in size. In this connection it should be emphasized that the gas conducted in the gas channel can also be an inert gas without added vapor and that this inert gas only exercises a tempering or even application-specific drying function.